Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/023—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets using multilayered plates or sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B38/00—Ancillary operations in connection with laminating processes
  • B32B38/0008—Electrical discharge treatment, e.g. corona, plasma treatment; wave energy or particle radiation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
  • B29K2023/04—Polymers of ethylene
  • B29K2023/06—PE, i.e. polyethylene
  • B29K2023/0608—PE, i.e. polyethylene characterised by its density
  • B29K2023/0625—LLDPE, i.e. linear low density polyethylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
  • B29K2023/04—Polymers of ethylene
  • B29K2023/08—Copolymers of ethylene
  • B29K2023/083—EVA, i.e. ethylene vinyl acetate copolymer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
  • B29K2023/04—Polymers of ethylene
  • B29K2023/08—Copolymers of ethylene
  • B29K2023/086—EVOH, i.e. ethylene vinyl alcohol copolymer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B38/00—Ancillary operations in connection with laminating processes
  • B32B38/0012—Mechanical treatment, e.g. roughening, deforming, stretching
  • B32B2038/0028—Stretching, elongating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
  • B32B2307/514—Oriented
  • B32B2307/518—Oriented bi-axially
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/724—Permeability to gases, adsorption
  • B32B2307/7242—Non-permeable
  • B32B2307/7244—Oxygen barrier
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/732—Dimensional properties
  • B32B2307/734—Dimensional stability
  • B32B2307/736—Shrinkable
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2323/00—Polyalkenes
  • B32B2323/10—Polypropylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2439/00—Containers; Receptacles
  • B32B2439/70—Food packaging
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/91—Product with molecular orientation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
  • Y10T428/1328—Shrinkable or shrunk [e.g., due to heat, solvent, volatile agent, restraint removal, etc.]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
  • Y10T428/2495—Thickness [relative or absolute]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2918—Rod, strand, filament or fiber including free carbon or carbide or therewith [not as steel]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31855—Of addition polymer from unsaturated monomers
  • Y10T428/31909—Next to second addition polymer from unsaturated monomers
  • Y10T428/31913—Monoolefin polymer
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31855—Of addition polymer from unsaturated monomers
  • Y10T428/31909—Next to second addition polymer from unsaturated monomers
  • Y10T428/31913—Monoolefin polymer
  • Y10T428/3192—Next to vinyl or vinylidene chloride polymer
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31855—Of addition polymer from unsaturated monomers
  • Y10T428/31909—Next to second addition polymer from unsaturated monomers
  • Y10T428/31928—Ester, halide or nitrile of addition polymer

Definitions

• the present invention relates to a multilayer, bioriented, heat shrinkable film, a method for the manufacture thereof and use thereof for packaging food products and consumer articles.
• the present invention relates to a multilayer, bioriented, heat shrinkable film extruded from a flat die and stretched both in machine direction and in cross-direction wherein at least one layer comprises at least one ethylene/alpha-olefin C 4- C 12 copolymer.
• Multilayer heat shrinkable films have been known for a long time.
• U.S. patent 4,532,189 discloses a multilayer, heat shrinkable film comprising:
• (B) two skin (external) layers comprising a blend of from 70% to 90%, by weight, of an ethylene/propylene copolymer and from 10% to 30%, by weight, of a propylene homopolymer; wherein said film has an average machine direction free shrink at 200°F of at least 12% and an average cross-direction free shrink at 200°F of at least 17%.
• the core layer may also comprise other polymers such as, for example, ethylene/propylene copolymers, ethylene/vinyl acetate copolymers, ionomer resins and non-Linear low density poly ethylenes.
• said film may also comprise two intermediate layers comprising a blend of approximately 90% by weight of an ethylene/vinyl acetate copolymer and approximately 10% of an ionomer resin.
• U.S. patent 4,551,380 discloses a multilayer heat shrinkable film comprising:
• (B) two surface layers comprising essentially a blend of (1) a linear Low density polyethylene, (2) a linear medium density polyethylene and (3) an ethylene/vinyl acetate copolymer.
• GB-A-2,097,324 discloses heat shrinkable films manufactured by stretching, at least three times their original linear dimension in at least one direction, a film having the following homogeneous composition:
• the films obtained with this technique have the disadvantage of not having sufficiently uniform thickness and planarity.
• the total thickness variation in said films is ⁇ 15% while, as regards planarity, it has defects consisting of deviations from a straight line (snaking) and sags. More particularly the average deviations from a straight line (snaking) is approximately 50 mm, whereas the average sag is approximately 35 mm.
• the tenter frame technique also known as "flat orientation technology” consists of extruding a film-forming material through a flat die over a chill roll, preferably immersed in water, to chill the molten film.
• the various polymers or blends of polymers are generally coextruded by conventional techniques but, when only a few of the layers have to undergo special treatments, such as for example irradiation with fast electrons to induce cross-linking, only the layer or layers to be treated is extruded or are coextruded, the tape obtained in this way is subjected to the required treatment and then the remaining layers are extruded on the same.
• the tape is then oriented, by stretching, in two separate and successive steps, although devices able to stretch the tape simultaneously in both directions are known (U.S. patent 3,148,409).
• MD machine direction
• TD cross-direction
• MD stretching is usually carried out by passing the tape through pairs of rolls which rotate at different speeds. At least one of the first pairs of rolls is heated, for example by inner circulation of hot oil.
• TD stretching is usually performed in a tenter frame oven which comprises a certain number of heating zones and suitable stretching means.
• a tenter frame oven comprises from three to six zones: one to two for preheating the tape, one to two for stretching it in the cross-direction and one to two for relaxing and winding the film.
• Each zone may be heated at a different temperature level.
• ethylene/alpha-olefin copolymer having a density of between 0.890 g/cm and 0.930 g/cm 3 , and (B) 25-0%, by weight, of a linear high density polyethylene having a density of between 0.935 and 0.960 g/cm 3 , with the proviso that the total of the film-forming polymer (A) and (B) has a single melting point as determined by
• EP-A-405 916 also refers to multilayer films, its examples only refer to monolayer films.
• multilayer films have, compared to monolayer ones, the considerable advantage of allowing to combine one with the other several layers having different physical and chemical properties in view of the required properties of the final film.
• the films manufactured by this technique have several advantages over those manufactured by the air bubble technique.
• a first advantage consists of the fact that the stretching ratios in machine direction and cross-direction may vary as required whereas in the air bubble technique they are always substantially equal one to the other.
• a second advantage is that the stretching ratio may be preselected within a relatively wide range, typically of betweeen 2:1 and 12:1, while in the air bubble technique it must be between 3:1 and 6:1.
• a further advantage consists of the fact that the thickness and planarity of the films manufactured by this technique are much more uniform than in those manufactured with the air bubble technique.
• An additional advantage is that, being able to control the thickness better, thinner films can be manufactured,
• a first object of the present invention is to provide a multilayer heat shrinkable film, extruded from a flat die and bioriented by the tenter frame technique, wherein at Least one layer consists of at least 50%, by weight, of an ethylene/alpha-olefin C 4 -C 12 copolymer or of a blend of ethylene/alpha-olefin C 4 -C 12 copolymers.
• a second object of this invention is to provide a multilayer heat shrinkable film wherein the total variation in thickness is Lower than ⁇ 10% and, preferably, than ⁇ 5%.
• a third object of this invention is to provide a multilayer heat shrinkable film wherein the average of the deviations from a straight line (snaking) is lower than 40 and, preferably, than 25 mm, and average of the sags is lower than 25 mm.
• a fourth object of this invention is to provide a multilayer heat shrinkable film which has been stretched with a stretching ratio of from 2:1 to 11:1 in machine direction and from 3:1 to 12:1 in cross-direction and, preferably, with a stretching ratio of from 4.5:1 to 9.5:1 in machine direction and from 5:1 to 11:1 in cross-direction.
• Another object of this invention is to provide a method for the manufacture of a multilayer heat shrinkable film having the above characteristics.
• a further object of this invention is to provide the use of a multilayer heat shrinkable film having the above
• T c chill roll temperature
• T p rolls temperature (°C) before longitudinal orientation
• T l rolls temperature (°C) during longitudinal orientation
• MD machine or longitudinal direction C .
• T cp preheating temperature (°C) in the cross-direction
• T cs stretching temperature (°C) in the cross-direction
• T cr relaxation temperature (°C) in the direction
• This property is measured by gradually heating the film and measuring the maximum force developed per section unit of the film itself.
• This property is measured by heating the film at 120°C for at Least 5 sec, and then measuring the percentage of shrinkage in the longitudinal direction and in the cross- direction.
• TTV total thickness variation
• PTV planarity variation The main planarity defects consist of bag & sag and snaking.
• the device used to measure these defects essentially consists of
• a feeler fixed to a sliding support unit provided with a scale for measuring the horizontal distance covered by the feeler from a prefixed zero point corresponding to the left edge of the film and a second scale for measuring vertical movements.
• the zero on this scale has been fixed by taking into consideration the natural drop midway in a perfectly flat film span,
• a roll of film is placed in the unwind section and a length of film is unwound.
• the unwind station is locked.
• the film is aligned and fixed to the wind-up core.
• the rewind section is Locked.
• the position of the flattest part of the film is measured.
• the bag and sag in the film are then measured by recording the difference between the film levels at each point and the level of the flattest part of the film.
• the data are reported on paper, i.e. sag and relevant position (left, center or right).
• the whole operation is performed twice to four times to measure from two to four lengths of film.
• Snaking also referred to as "banana effect" represents the deviation of film from a straight line for a given
• the measurements are performed on a length of film of 4 metres using the device and method described above.
• Cross-Linking is measured according to ASTM D 2765-90.
• Mrad denotes the dose absorbed by the tape or by the film during treatment of irradiation with high energy electrons, and is equivalent to 10 4 J/Kg.
• film means a flat and flexible material having a thickness of between 5 and 150 microns.
• heat shrinkable film means a bioriented film which shrinks by at least 15% at 120°C in both directions.
• tape means a layer of material before orientation and has typically a thickness of between 180 microns and 3 mm.
• polyolefin means thermoplastic resins obtained by homopolymerisation or copolymerisation of olefins with other monomers, wherein the olefin units are present in larger amounts than other monomers.
• polyolefin comprises but is not limited to "ethylene/alpha-olefin copolymer", "ethylene/vinyl acetate (EVA) copolymer”, “ethylene/acrylate copolymer”, “propylene copolymer” and “polypropylene” (PP) as defined hereinafter.
• modified polyolefins means polyolefins
• ethylene/alpha-olefin copolymer means a copolymer of ethylene and one or more C 4 -C 12 alpha-olefins and is preferably selected from the group comprising linear copolymers of ethylene and butene-1, 4-methyl-pentene-1, hexene-1 or octene-1.
• ethylene/vinyl acetate (EVA) copolymer means an ethylene/vinyl acetate copolymer wherein the ethylene units are present in Larger amounts than the vinyl acetate units.
• ethylene/acrylate copolymer means a compound obtained by copolymerisation, according to known techniques, of ethylene with acrylic monomers of the formula where R is H or C 1 -C 4 alkyl, and
• X is H, C 1 -C 4 alkyl or a metal cation, preferably chosen from Zn ⁇ and Na ⁇ ,
• polystyrene resin means a copolymer of
• polypropylene means a thermoplastic resin obtained by homopolymerisation of propylene according to conventional techniques.
• polyolefins modified polyolefins and blends thereof, with the proviso that this layer has more than one melting point as determined by differential scanning calorimetry according to ASTM D-3418.
• the present invention relates therefore to a multilayer, bioriented, heat shrinkable film extruded from a flat die wherein at least one layer comprises an ethylene/alpha-olefin C 4 -C 12 copolymer, characterised in that: (a) said layer comprises
• polyolefins modified polyolefins and blends thereof, with the proviso that this layer has more than one melting point as determined by differential scanning calorimetry according to ASTM D-3418,
• the total variation in thickness of said film is lower than ⁇ 10%
• the average deviation from a straight line (snaking) of said film is less than 40 mm.
• the polyolefins are preferably selected from ethylene/vinyl acetate copolymers, ethylene/acrylate copolymers, propylene copolymers and polypropylenes.
• copolymerisation process quantity of the alpha-olefin, nature of the catalyst, comonomer feed rate, temperature and other process conditions which may have a significant effect on the distribution of the alpha-olefin in the copolymer chains.
• alpha-olefins examples include butene-1,
• the content of alpha-olefin in the ethylene/alpha-olefin C 4 -C 12 copolymer is preferably of at least 7%, by weight, and the alpha-olefin is octene-1.
• the ethylene/alpha-olefin C 4 -C 12 copolymer is a linear ethylene/octene-1 copolymer which has a octene-1 content of 10% ⁇ 2%, by weight, a density of circa 0.920 g/cm and three melting points at 106 ⁇ 2; 119 ⁇ 2 and 122 ⁇ 2°C.
• the layers comprising an ethylene/alpha-olefin C 4 -C 12 copolymer are the core layer of a film having three layers or the skin layers of a film having five layers.
• intermediate layers of a five-layer film may have a composition which is different one from the other. Nevertheless, they preferably have the same composition and essentially consist of one or more film-forming polymers chosen from among ethylene/vinyl acetate copolymers, ethylene/acrylate copolymers, polypropylene, polypropylene copolymers, modified polyolefins and bLends thereof.
• the method for manufacturing a multilayer, bioriented, heat shrinkable film according to the present invention comprises, preferably, stretching of the film, at appropriate
• multilayer, bioriented, heat shrinkable film according to the present invention for packaging articles is of the conventional type: the film is wound around the article, sealed or clipped and shrunk.
• Fig. 1 is a cross section of a first preferred embodiment according to the present invention consisting of a three-layer bioriented film.
• Fig. 2 is a cross section a second preferred embodiment according to the present invention consisting of a five-layer bioriented fiIm.
• Fig. 1 is a cross section of a preferred bioriented, three-Layer film according to the present
• this embodiment comprises a core layer 2 and two skin layers 1 and 3.
• the thickness of the film is of from 8 to 25 microns.
• the preferred thickness of the core or internal layer is in the range of from 1 to 23 microns whereas that of each of the skin (external) Layers is in the range of from 1 to 12 microns.
• the core Layer comprises
• this layer has more than one melting point as determined by differential scanning calorimetry according to ASTM D-3418.
• the core layer comprises 100%, by weight, of an ethylene/alpha-olefin C 4 -C 12 copolymer or a blend of
• ethylene/alpha-olefin C 4 -C 12 copolymers which have more than one melting point as determined by differential scanning calorimetry according to ASTM D-3418.
• a typical example of film-forming composition suitable for forming the layer 2 of Fig. 1 consists of 100% of an
• ethylene/octene-1 copolymer which contains 10% of octene-1 and has a density of 0.920 g/cm 3 and three melting points at 106 ⁇
• the film-forming composition of the core layer will contain up to 25%, by weight, of a polymer chosen from polyolefins, modified polyolefins and blends thereof.
• both the skin layers 1 and 3 of Fig. 1 have the same composition and essentially consist of a polymer chosen from ethylene/vinyl acetate copolymers, ethylene/acrylate copolymers, polypropylenes, polypropylene copolymers, modified polyolefins and blends thereof.
• polystyrene resin examples include ethylene/alpha-olefin C 4 -C 12 copolymers, propylene copolymers and polypropylenes.
• composition for both layers 1 and 3 of Fig. 1 is the following:
• a second typical example of film-forming composition suitable for both layers 1 and 3 of Fig. 1 is the following: - 75-100%, by weight, of a copolymer of propylene, - 0-25%, by weight, of a polypropylene (PP).
• PP polypropylene
• the second preferred embodiment shown in Fig. 2 relates to a five-ply barrier film of this invention comprising a core Layer 2, two tie (or intermediate) layers 4 and 5, and two skin layers 1 and 3.
• the thickness of this film is of from 15 to 45 microns.
• the core layer 2 of the embodiment shown in Fig. 2 acts as a barrier against oxygen permeation and is made of any of the known barrier polymeric resins, such as ethylene/vinyl alcohol copolymers (EVOH) and vinylidene chloride copolimers (PVDC).
• EVOH refers to saponified products of ethylene/vinyl ester copolymers, generally of ethylene-vinyl acetate
• the EVOH can be employed as such or blended with other EVOHs or with one or more polyamides.
• the term PVDC refers to a vinylidene chloride copolymer wherein a major amount of the copolymer comprises vynilidene chloride and a minor amount of the copolymer comprises one or more unsaturated monomers copolymerizable therewith, typically vinyl chloride, and alkyl acrilates (e.g. metyl acrylate) or to a blend thereof in different proportions.
• said PVDC will contain plasticisers and/or
• composition of the two tie layers 4 and 5 of the embodiment shown in Fig. 2 may be the same or different.
• tie layers 4 and 5 have the same composition and are made of a modified polyolefin.
• a typical example of film-forming composition suitable for forming the layers 4 and 5 of Fig. 2 consists of 100% of a maleic anhydride grafted ethylene/butene copolymer containing
• both skin layers 1 and 3 of the embodiment shown in Fig. 2 have the same composition and comprise
• the skin layers 1 and 3 of the second preferred embodiment of Fig. 2 comprise 100%, by weight, of an ethylene/ alpha-olefin C 4 -C 12 copolymer or a blend of ethylene/alphaolefin C 4 -C 12 copolymers which have more than one melting point as determined by differential scanning calorimetry according to ASTM D-3418.
• a typical example of a film-forming composition suitable for forming the layers 1 and 3 of Fig. 2 consists of 100% of an ethylene/octene-1 copolymer which contains 10% of octene-1 and has a density of 0.920 g/cm and three melting points at 106 ⁇ 2; 119 ⁇ 2 and 122 ⁇ 2°C.
• a second prefe rred embodi ment according to Fig. 2 it may be advantageous to recycle the remains of film-forming composition and scraps, of tape and/or film, which are generated during the various steps of the manufacturing process, adding them to the film-forming composition for the skin layers 1 and 3 or, preferably, for the intermediate layers 4 and 5.
• additional inner layer(s) can be formed composed exclusively of recycled film.
• the film will contain up to from 30% to 40% by weight, preferably up to 25%, even most preferably from about 7% to about 20% of recycled material.
• composition suitable for manufacturing a multilayer, bioriented, heat shrinkable film according to the present invention is the following:
• a second specific example is the following: Film-forming composition of the core layer 2 ( Fi g . 1 ) :
• polypropylene having a density of 0.904 g/cm and a single melting point at 160°C;
• composition suitable for manufacturing a multilayer, bioriented, heat shrinkable film according to the present invention is the following:
• Film-forming composition of the skin layers 1 and 3 (Fig. 2): - 50.1%, by weight, of an ethylene/octene-1 copolymer which contains 10% of octene-1 (NMR determination) and has a density of 0.920 g/cm and three melting points at 106 ⁇ 2; 119 ⁇ 2 and 122 ⁇ 2°C;
• the skin layers 1 and 3 have more than one melting point and come within the scope of the present invention.
• Suitable slip agents are erucamide (available from Humko Chemical under the trademark Kemamide E) .
• Other examples of suitable slip agents are stearamide (available from Humko Chemical under the trademark Kemamide S) and N,N'-dioleoylethylenediamine (available from Glyco Chemical under the trademark Acrawax C).
• a suitable anti-block agent is represented by diatomaceous silica (available from McCullough 8 Benton, Inc. under the trademark Superfine Superfloss).
• Other suitable anti-block agents are synthetic silicas such as those
• antioxidants As is well-known to those skilled in the art, other suitable additives for film-forming compositions are antioxidants, heat stabilisers, organic or inorganic coloured pigments, anti-fog agents, anti-static agents, UV absorbers and the like.
• the extruded and cooled tape is irradiated, before stretching, with high energy electrons. Said irradiation may however also be performed during or after stretching.
• this type of irradiation causes cross-linking of the polymers and improves their mechanical properties, especially at high temperatures.
• the preferred level of radiation is of from 1 to 12 Mrad. Even more preferably the level of radiation is of from approximately 1.5 to approximately 5 Mrad.
• the preferred conditions for orienting the multilayer films of the present invention comprise first of all stretching in machine direction at a temperature of from 60 to 150°C, preferably of from 80 to 120°C, and then stretching in cross-direction, preheating the film to a temperature of from 80 to 190°C, preferably of from 110 to 170°C, stretching it at a temperature of from 60 to 160°C, preferably of from 80 to 140°C, and, finally, relaxing it at a temperature of from 50 to 150°C, preferably of from 75 to 130°C.
• the stretching ratios according to the invention range from 2:1 to 11:1 in machine direction and from 3:1 to
• the multilayer, bioriented, heat shrinkable film of the present invention is characterised by a total thickness variation lower than ⁇ 10%. Typically said total variation in thickness is lower than ⁇ 5%.
• the film according to the present invention is characterised in that the average deviation from a straight line (snaking) is smaller than 40 mm and that the average sag is smaller than 25 mm.
• the preferred use of the multilayer, bioriented, heat shrinkable film according to the present invention consists of packaging articles of various types. Preferably food products and consumer articles.
• the film is wound around the article, sealed or clipped and shrunk according to conventional techniques. For example, by exposing the article wound in the film to a current of hot air or hot water.
• the aforesaid blend of layers 1 and 3 has two melting points at 102.1 and 120.5 ⁇ 2°C.
• the film-forming compositions were coextruded through a flat die and the cast tape was chilled on a chill roll partially immersed in a water bath at a temperature of from 5 to 60°C
• the tape was then heated to a temperature of from 110 to 115°C on oil heated rolls stretching the tape in machine direction with ratios of from 6:1 to 9.5:1.
• the tape was then transferred to a tenter frame oven having four heating zones in which the temperature was of from 115 to
• the multilayer bioriented films obtained in this way have a thickness of 15 microns.
• the ratio between layers 1, 2 and 3 was 1:2:1, respectively.
• the process conditions (PC) of Examples 1-5 and the physical properties (FA) of the films manufactured are shown in Table A below.
• the film-forming compositions were coextruded in the form of a tube.
• the extruded tube was heated and inflated into a bubble by applying an internal air pressure and thus transforming the narrow, thick-walled tube into a wide, thin-walled tube.
• tubular film was cooled and collapsed into a superimposed lay-flat tape and wound onto cylinders.
• the air bubble process orients the film by stretching it simultaneously both longitudinally and transversely, thus imparting shrinkability.
• the comparison film obtained in the best working conditions known to the inventors had a thickness of 15 microns and will be denoted hereinbelow by the code C-1.
• MD and TD shrinkage values which may differ one from the other within a wide range, are worthy of note.
• Example 13 4 zones of the tenter frame oven have been devoted to preheating, 2 zones to stretching and no zone to relaxation;
• Example 14 1 zone of the tenter frame oven has been devoted to preheating, 2 zones to stretching and 3 zones to relaxation.
• the film-forming composition of examples 1-5 was used, changing the stretching conditions as indicated in Table G which also reports the properties of the thus obtained films.
• the manufacturing line speed was also increased to reduce the thickness of the films to 12 and 10 microns respectively.
• the same configuration of the tenter frame oven has been employed in these three examples: 2 preheating zones, 2 stretching zones and 2 relaxation zones.
• a propylene/ethylene copolymer which contains 3.5% ethylene and has a density of of 0.900 g/cm 3 and a single melting point at 135.9 ⁇ 2°C; - 12.1%, by weight, of polypropylene having a density of 0.904 g/cm and a single melting point at 160 ⁇ 2°C;
• the abovementioned blend of layers 1 and 3 has one melting point at 128 ⁇ 2°C.
• the ratio between Layers 1, 2 and 3 was 1:3:1, respectively.
• the film manufactured in this way had a thickness of 15 microns and is denoted hereinunder by the code C-2.
• the physical properties (FA) of the film C-2 and the working conditions of its manufacturing process (PC) are shown in Table H in comparison with those of the films of Examples 21-23 of the invention.
• Film-forming composition of the core layers 1 and 3 (Fig. 1): - 87.5%, by weight, of a propylene-ethylene-butene-1 terpolymer containing 94% propylene, 4% ethylene and 2% butene-1, m.p. 130 ⁇ 2°C;
• polypropylene having a density of 0.904 g/cm and m.p. 160 ⁇ 2°C;
• the ratio between layers 1, 2 and 3 was 2:11:2 respectively.
• the same general process described in examples 1-5 was used, changing however the stretching conditions as indicated in Table I which also reports the properties of the films thus obtained.
• polypropylene having a density of 0.904 g/cm and m.p. 160 ⁇ 2°C;
• the ratio between layers 1, 2 and 3 was 2:11:2 respectively.
• the same general process described in examples 1-5 was used, changing however the stretching conditions as indicated in Table I which also reports the properties of the films thus obtained.
• the ratio between the five Layers was 2:2:1:2:2.

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